Quiet a lot of people image DSO's using a large Dob with servocat/Argo combo. Or other goto option.
http://homepages.uni-tuebingen.de/jo...r/Galaxies.htm
http://www.obsessiontelescopes.com/imaging/index.html
Planning is the key to avoid field rotation, you need to study the subject and when it would be the best time to image it to avoid FR. You can use Field derotators as you have mentioned.
If the drive system is designed correctly you can also avoid PEC and backlash.
Regards
Fahim